The invention relates to a MOS-gate switchable power semiconductor component with a semiconductor body, having a plurality of unit cells, arranged side-by-side and switched parallel, which form a thyristor, and which comprise a p-emitter zone adjacent to the anode, an adjoining weakly doped n-base zone, followed by a connecting p-base zone that is joined by a n-emitter zone, into which pairs of p+-zones are embedded and which, together with the n-zone between them and an insulating gate arranged above, form a lateral first p-channel MOSFET, wherein on the one hand the drain area on the edge of the emitter zone is connected to the external cathode, which has no contact with the n-emitter zone, and on the other hand, the inside source area has a floating contact which makes simultaneous contact with the n-emitter zone, and wherein a second p-channel MOSFET is formed from the p+-zone that makes contact with the external diode, the surface area of the p-base zone and the intervening n-emitter zone, together with an insulating gate.
Such a power semiconductor component is known from DE 41 26 491. With this power semiconductor component, a p-channel MOSFET is integrated into the n-emitter zone of the thyristor, which channel is formed by two embedded p+-zones as source and drain area, as well as the MOS gate arranged above the n-conducting intervening region. The drain p+-zone at the edge of the n-emitter zone is connected to the cathode as contact electrode. The source p+-zone and the adjacent section of the emitter zone are equipped with a floating metal contact, which has an ohmic connection to the thyristor and the MOSFET, so that they are connected in series. A second p-channel MOSFET M2 is formed by the p-base of the thyristor, which extends to the surface, the p+-zone at the edge of the n-emitter zone, which makes contact with the cathode, as well as the n-emitter zone segment located in between, with the above-arranged insulating gate G2.
In order to shut down the component, the MOSFET M1, which is connected in series with the thyristor, is turned off while the MOSFET M2 is switched on simultaenously, thereby creating a secondary path from the p-base of the thyristor to the cathode. For this, the gates of the two MOSFET channels must be triggered with different gate signals. In order to achieve good shutdown behavior and a large, secure operating area (SOA) during the shutdown, both gate signals must be synchronized precisely as to time and absolute values. Interferences in the correlation of gate signals will reduce the operating area, and the component can easily be destroyed. Because a considerably more involved driver electronics is necessary, the shut-down via two gates with various control signals that must be synchronized, represents a great practical disadvantage as compared to other components, such as the IGBT. Another disadvantage is that the component does not have a characteristic with current saturation, meaning that the current does not tend toward a saturation value with increasing voltage. Thus, in case of a load short-circuit, the current is not limited by the component itself, so that fuses must be connected in series to prevent a destruction in case of a short circuit. This also applies if one of the gate connections and the cathode connection are linked on the outside. As a result of the inside resistance of the gate cathode circuit, caused among other things by the semi-insulated polycrystalline gate, the gate will not remain on the cathode potential in case of a rapid current and voltage rise. In other words, the component is not short-circuit proof.
In order to ignite the thyristor, a third and externally triggered MOSFET is integrated for the switching on of the component known from DE 41 26 491 A1. This MOSFET, which is designed as n-channel MOSFET of the enhancement type (normally-off) combines the n-emitter zone with the n-base of the thyristor when it is switched on. To switch on the component, the first and the third MOSFET are switched on and the second MOSFET is shut off. The additional gate needed for the switching on further increases the required expenditure for the driver electronics.
Field-effect controlled power semiconductor components, in the following also called components, are already used on a large scale in practical operations in the form of power MOSFETs and the insulated gate bipolar transistors (IGBT). The on-state voltage of MOSFETs increases strongly with the rising off-state voltage, for which they are dimensioned, because of the missing conductivity modulation, so that MOSFETs can only be used up to about 500 V. The IGBT as bipolar component exhibits a better on-state behavior with off-state voltages above 300 V than a MOSFET. However, compared to the MOS controlled thyristors, such as the component according to DE 41 26 491 A1, the on-state behavior of the IGBT above approximately 600 V blocking capacity is worse because its on-state and off-state characteristic features are determined by a bipolar transistor and not a thyristor. The switchable current per chip surface is therefore smaller than with the component according to DE 41 26 491. One advantage of the IGBT is, however, that it can be turned on and off by a gate, identical to the power MOSFET, and has a characteristic with current saturation.
Known are also special MOS-controlled thyristors (MCTs), comprising a MOSFET integrated into the n-emitter zone, which opens a secondary path from the p-base to the cathode when switched on, thereby shutting down the component. The shutdown behavior of this component, however, is impaired by the current filamenting. The on-state characteristic for the MCT is similar to that of a standard thyristor, meaning it does not have current saturation. That is why the MCT is not "short-circuit proof" either, which is viewed as a considerable disadvantage as compared to the IGBT. Above all, however, MCTs did not succeed in practical operations because of the current filamenting.
Another MOS-controlled thyristor, which is called an "emitter-switched thyristor" or EST was described in articles by Baliga et al.; see IEEE Trans. Electron Devices 38 (1991), p. 1619. With the EST, a MOSFET is integrated into the p-base of the thyristor and is connected in series with the thyristor structure. The EST shuts down if the MOSFET is shut down. One disadvantage of this component is that it contains a parasitic thyristor that makes contact with the cathode. In order to prevent this thyristor from switching on, the p-base, together with the n-emitter, is contacted through the cathode metallization, meaning it is short-circuited with the cathode. As a result of this, however, the floating main thyristor is prevented from engaging as well until it reaches a considerable distance from the short-circuit location. The individual component therefore must have a relatively large lateral dimension, so that the MOS channel width that can be reached for each semiconductor surface and thus also the switchable current per surface are strongly reduced here as well. As a result of the MOSFET connected in series, the characteristic hints at a current limitation. This limitation is not very distinct because, under normal operating conditions, the MOSFET is already entering the breakdown before the transition between p-base and n-base, which permits a higher voltage, starts to block significantly.
It is the object of the invention to improve the design of an MOS-controlled power semiconductor component of the above-described type in such a way that it can be shut down by a single gate and that it has a characteristic with current saturation. Furthermore, the power semiconductor component is to be improved such that it can be switched on with this gate as well.